Soil seed banks in degraded and revegetated grasslands in the alpine region of the Qinghai-Tibetan Plateau

Abstract

To assess the role of soil seed banks in restoring degraded grasslands in the alpine region of the Qinghai-Tibetan Plateau (QTP), we studied the similarity of species composition between aboveground vegetation and soil seed banks in alpine grasslands at different degradation levels and in revegetated grasslands in different years since restoration across different seasons (spring, summer and autumn). One-way analysis of variance (ANOVA) was applied to compare differences in the soil seed bank among the native grasslands in different degraded states, in the revegetated grasslands across years since restoration and seasonal changes. The Sorenson similarity index and detrended correspondence analysis (DCA) were applied to examine the similarity of species composition in the soil seed bank and aboveground vegetation. It was found that the highest and lowest soil seed density occurred in autumn (October) and summer (July), respectively. We also explored the changes about transient and persistent soil seed banks. Basically, we found that all experimental plots were inclined to choose transient seed banks rather than persistent seed banks expect for non-degraded and 5 year restoration grasslands. There were significant differences in soil seed density among the degraded grasslands and among the different aged revegetated grasslands (P<0.05). Soil seed density increased with decreasing levels of degradation while it increased with age since restoration. We also explored the seed density among three functional groups (grasses, sedges and forbs) and found that forbs had the highest soil seed density. A low similarity of species composition between soil seed banks and aboveground vegetation in the degraded grasslands implied that the seed bank contributed little to the restoration of the aboveground vegetation in these degraded grasslands. A high similarity of species composition between soil seed banks and aboveground vegetation in the artificially restored grasslands indicated that the seed soil bank was important in maintaining the vegetation structure and cover in the established grasslands.